This application relates to a turbine engine assembly, and more particularly to a fuel delivery system for such an engine. It will be appreciated, however, that the system may find application in related systems or environments requiring high reliability, low cost, and low weight without sacrificing performance.
Presently available fuel delivery systems typically use a centrifugal boost stage that directs pressurized fluid into a filter and then through a gear stage or gear pump. The fuel is subsequently directed to a metering valve and into a pressurizing valve where it ultimately leads to fuel nozzles associated with the turbine engine. The centrifugal boost stage provides pressure and flow to adequately fill the high pressure stage with a homogenous liquid fuel, i.e., no vapor, under varying pump inlet conditions. For example, pump inlet conditions may include low pressure, high temperature, etc. In addition, the centrifugal boost stage serves as a sink for bypass fluid from the fuel control and provides a reference base pressure for use in the fuel control.
The high pressure positive displacement stage is typically a gear pump. The gear pump provides a positive flow to the system regardless of the system restriction, that is, up to a set point of a relief valve. The high pressure relief valve is incorporated in the main engine pump to protect the fuel system. Bypass flow is also provided prior to directing fuel through the metering valve. The bypass flow recirculates fuel back to the pump. The amount of bypass fuel is controlled by sensing on either side of a metering valve with a head regulator that provides an appropriate signal to a bypass valve. In addition, the system will typically use some of the pressurized fuel for actuator use.
Although these systems have proven effective to date, improvements in the acquisition and operating costs are deemed desirable. In addition, improved efficiency, life expectancy, and in particular greater efficiency at the idle descent over conventional systems is desirable. A reduction in the number of components used to meter fuel and control engine overspeed is also desirable. Moreover, reducing the number of system heat exchangers would serve all of the above-noted goals, as well as provide a significant reduction in engine level piping.
With the known systems, there is a need to supply the actuators as well as the fuel nozzles. With this dual role, a concern for transient flow demand from the actuation system must be accounted for. If a large demand is required for actuation supply, then overall demand from the pump is large and the fuel nozzle is inadequately served resulting in engine flame out. On the other hand, if more fuel is supplied to the fuel nozzle than is necessary, for example, when the actuator demand is reduced, then the engine is potentially subject to a stall.
Thus, in known systems there are generally three output paths from the pump. One path is directed to the metering valve, a second path to the actuators, and a third path for bypass purposes. This is similar to having three orifices disposed in parallel relation. In other words, a flow change in one orifice does not result in a big flow change in the other two. But, if a variable flow pump is used, the system reduces to the equivalent of two orifices and thus flow change in one results in a large flow change in the other orifice. Thus, a need exists for the pump to make this deficiency up quickly, i.e., a fast response. While others in the past have used the bypass as an attempted solution, this adds more components, rather than less components as is always desired.
An improved fuel delivery system providing for high efficiencies, fewer components, and increased reliability is provided.
According to one embodiment of the invention, a variable flow pump is operatively associated with a metering valve having closed loop mass flow control. The mass flow controller monitors pressure on either side of the metering valve and alters pump output in response thereto.
Another embodiment of the invention incorporates thermal management control of the pump fluid. Particularly, fluid exiting the pump is fed through a heat exchanger before being split between a thermal control valve and a downstream actuator use. If the system detects that a portion of the fluid needs to be recirculated for thermal purposes, the thermal control valve is opened to a desired level.
Preferably, a transducer monitors the pressure across the metering valve and a temperature probe provides desired data of the fuel temperature directed toward the actuation use.
A primary benefit is a closed control loop on delivered fuel mass flow instead of just a metering valve position.
In addition, an electrical overspeed system can be responsive to trip or shut-off, trim or upper speed limit, and/or governing functions such as speed settings.
Many components used in present systems are either combined or eliminated. For example, the bypass valve, head regulator, and logic select valve function are eliminated from a conventional fuel controller architecture. Three heat exchangers in the main, servo, and integrated drive generator (IDG) portions of the system are combined into a single unit.
A primary advantage of the invention resides in the ability to use a single loop control of mass flow that is proportionally controlled.
A substantial improvement in fuel delivery is achieved without increasing the number of components or overall complexity of the system.
Still another advantage resides in the ability to retrofit existing systems.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description.